Method of fabricating a grid electrode



Jan. 13, 1959 A A. R. BOLZ 2,369,015

METHOD OF FABRICATING A GRID ELECTRODE Filed July 1, 1955 FIG.

PLACE SIDE RODS IN WINDING MEANS APPLY CROSS STRAPS TO THE SIDE RODS TOFORM A RIGID GRID FRAME ASSEMBLY WIND SECOND HEL IX OF GRID WIRE AROUNDTHE FRAME IN THE SPACES PROVIDED BY ADJACENT TURNS OF THE FUSIBLEMATERIAL APPLY HEAT 7O GRID ASSEMBL Y TO MELT THE FUSIBLE MATERIAL ANDSECURE THE GRID WINDING TO THE FRAME 3 IN PROPER SPACED 7 RELATIONSHIPFIG. 4

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INVENT'OR A. R. BOL Z A T TORNEV METHOD OF FABRICATING A GRID ELECTRODEAlfred R. Bolz, Lutherville,,Md.,. assignor to American Telephone andTelegraph Company, a corporation of New York Application July 1, 1955,Serial No. 519,328 9 Claims. (Cl. 313-350) The invention relates tospace discharge devices and more particularly to a grid assembly and itsmethod of fabricating such devices.

The operating requirements of many present-day types of space dischargedevices are such that in these devices there must be an extremelyprecise mechanical correlation of the elements of the electrode assemblyinvolved. Some desirable characteristics, such as hightransconductanceand low noise, are directly dependent upon the reliability of thespacing of the control grid wires with respect to each other and withrespect to the other electrodes of the assembly. I

In discharge devices designed to operate in the higher frequency ranges,for example, in order to secure the desired controlling action upon theelectron stream needed for high values of transconductance, it isadvantageous that the grid laterals be relatively close together andspaced uniformly along the length of the grid. It is furtheradvantageous that the grid laterals mounted on the grid framebe firmlysecured thereto to avoid undesirable effects of electrostatic fields ormechanical vibration upon the grid pitch.

The above-recited conditions have presented some rather difiicultmechanical problems in the prior art of grid fabrication. Suchwell-known methods of spacing and securing grid wires to a frame asnotching and swaging or using welded metal joints have not provedentirely In accordance with a feature of this invention, a thread ofthin fusible material is wound upon the support rods of a grid frame toenable the turns of a grid Wire to be easily and properly locatedthereon in adesired spaced relation to one another.

It is a further feature-of this invention that the thread of thinfusible material subsequently be heat treated to bond the turns of gridwire to the frame in the desired spaced relation.

A complete understanding of this invention, together with theabove-noted and other features thereof, may be gained from considerationof the following detailed description and the accompanying drawing, inwhich:

Fig. 1 is an elevational view of an illustrative discharge deviceincorporating a grid assembly fabricated in accordance with thisinvention, a portion of the envelope and the internal structure of thedevice being broken away to show the grid assembly;

Fig. 2 is a chart showing the steps constituting a method of fabricatinga grid in accordance with one specific embodiment of this invention;

Fig. 3 is a partial elevational view of one side rod of the gridassembly after the fusible material and grid are wound prior to thefinal processing; and

Fig. 4 is a perspective view of the grid in final form with the fusiblematerial fired and the assembly prepared for insertion in the unitaryelectrode assembly in Fig. 1.

Referring now to the drawings, Fig. 1 discloses an' electronicdischargedevice of the type in which the invention advantageously may beutilized. Such device may comprise an electrode assembly including acontrol grid I wound about a pair of side rods 2 and 3, a screensatisfactory due to the difficulty in obtaining small spacings in theformer and in utilizing high melting point metals in the latter.Further, it was a difficult and timeconsuming task with such methods toobtain an exact and uniform spacing of the grid laterals.

t It is an object of this invention to provide an improved method offabricating grid assemblies for space discharge devices wherein theturns of a grid wire may be accurately and relatively easily spaced andsecured on a grid frame.

It is a further object of this invention to enable utilization of themeans for initially. spacing the grid wire turns subsequently forsecuring the turns to the grid frame in a desired spaced relation toeach other.

illustrative embodiment of this invention in which the side rods of thegrid frame structure are wound with a helix of a thin fusible materialin continuously contact- .55 It is a still further object of thisinvention to realize lineal inch of side rod.

grid 4 surrounding the control grid l and wound about a pair of siderods 5 and 6, and an anode 7. The entire electrode assembly is supportedbetween a pair of transverse mica end spacers S and 9, the lowermost oneof which is held in position by a number of support members 10 which arefixed to the inner base member 11 of the envelope 12. Electricalconnection from the exterior of the envelope to the electrodes is madeby the pins 13, which extend through the base of the envelope and aresealed therein, and the straps 14 extending from the pins to the variouselectrodes. The discharge device further may include a getter 15 and anend shield 1% as shown in Fig. 1.

The control grid 1 of the discharge device shown in Fig. l is made up ofa plurality of turnu of a fine grid wire wound on a frame whichadvantageously may comprise the pair of side rods 2 and 3. These siderods advantageously are rigidly maintained in proper spaced relationwith respect to each other by a pair of cross straps 16 and 17 locatednear the ends of the side rods as best seen in Fig. 4

In accordance with one embodiment of this invention, the grid isfabricated in the manner shown by the chart of Fig. 2. The side rods ofthe grid frame first are placed in a winding machine, such as is knownin the art, and a helix of thin fusible material 18, whichadvantageously may be glass thread, is wound upon the side rods toprovide the requisite number of turns per In accordance with a furtheraspect of this invention, the glass thread thus utilized has ingrelation therewith to provide the requisite; numberof turns per linealinch of the supporting rods. ,The grid wire then is wound about the rodsin alternate or interposed relation with the fusible material, thespaces between adjacent convolutions of the latter serving to locate thesuccessive turns of the grid wire and determining terials used. a

the desired number of turns per lineal unit. The entire-..

assembly then is heat treated to fuse the fusible, helix materialsufficiently to bond the turns of the grid wire securely in the desiredposition.

a coeflicient of expansion matching that of the grid ma- For example, inthe specific illustrative embodiment shown in Figs. 3 and 4 of thedrawing, wherein the grid is of tungsten and the frame side rods ofmolybdenum, a glass having properties similar to that commerically knownas Corning No. 7052 advantageously may be employed. This is aborosilicate glass which is composed of the following approximate parts:silica 68.0, alumina 8.1, sodium oxide 1.9, barium oxide 2.4, lithiumoxide 8.5, and boron oxide 15.2, and has a coefi'lcient of expansionsubstantially equal to 4.7 10" centimeters per centimeter length perdegree centigrade.

In accordance with one specific embodiment of this invention, a pair ofcross straps 16 and 17, which advantageously may be comprised ofmolybdenum, is then fastened to the ends 'of the side rods providing arigid and unitary grid frame structure. A helix of fine grid wire thenis wound about the side rods of the grid frame, the spacesbetweenadjacent convolutions of the glass thread servingproperly' tolocate the successive turns of the grid wire and to determine thedesired number of turns per lineal inch of side rod.

The entire grid assembly then is heat processed, such as by placing theassembly in an electrically heated oven for a suflicient time to causethe thread of fusible material to fuse and permanently bind the turns ofthe grid wire to the grid frame at the desired spacing.

This arrangement provides an efficient assembly wherein the helicalgridwinding is relatively easily spaced and secured to the grid frame. Thespacing between adjacent turns of the grid wire is controlled ina simplemanner l1 rality of turns of a fusible material around a frame, windinga grid wire upon said frame, said grid wire being positioned betweenadjacent ones of said turns, and heating said electrode assembly tocause said fusible material to secure said grid wire to said frame.

3. The method of spacing a grid wire on a frame in an electrode assemblycomprising thesteps of winding a helix of a fusible material on saidframe to provide a desired number of turns per lineal unit of saidframe, and winding ahelix of grid wire on said frame in the spacesbetween adjacent convolutions of the fusible material to space properlysuccessive turns of said grid wire.

4. The methodof spacing a grid wire on a frame in I an electrodeassembly in accordance with claim 3 further through the choice of athread of fusible material of proper diameter. Furthermore, the heattreatment incidental to the fusing process is notseriously detrimentalto the tension stress of the fine grid wire or the frame structure.since these components advantageously are highly refractory metals, thusresulting in very little loss in the residual tension. 1

Fig. 3.- shows a partial view of the grid assembly com- 0 prising theside rod3, the turns of'the grid wire 1, and the turns of the fusiblethread 18 prior to heating of the grid assembly to fuse the thread 18.In accordance with an aspect of the invention the diameters of the gridwire and the fusible thread advantageously are of the same diameter, as,for example, .001 inch each, thus enabling a grid of 500 turns per inchto be wound around the side rods in the region between the cross straps.

It can now t be seen that due to the advantages obtained by this highlyefficient method of construction grids having very close spacings may beconstructed with sufiiciept precision to satisfy the electricalcharacteristics required in present;

day discharge devices.

Fig. 4 shows the completed grid assembly after the heat treatment hascausedthe grid laterals 1 to be fused to the side rods 2 and 3 in thedesired spaced relation. The grid assembly as shown is in condition tobe inserted in the discharge device in the manner shown by the unitaryassembly of Fig. 1.

Whilethis invention has been disclosed in a particular embodiment andmethod of operation, it will be undercomprising the step of heating theframe for a sufficient time to cause the fusible material to bond thegrid wire to the frame in the desired spaced relation.

5. A composite electron discharge grid assembly com. ,prising a supportmember, a thin Wire of fusible material wound about said support incontinuously contacting relation .therewithdefining positioning means onsaid support, anda helix of grid wire wound about said support insuccessively interposed relation with adjacent turns of said thin:fusible material, each turn of the helix contacting adjacent turns ofthefusible material.

6. A .composite electron discharge grid assembly in accordance withclaim 5, wherein said helix of thin, fusible material has a-coefiicientof thermal expansion substantially equal to that of said support memberand grid wire.

7. A composite electron-discharge grid assembly comprising a pair ofside supports, a helix of thin, fusible material wound about each ofsaid supports in continuously contacting:relation therewith, adjacentturns of said thin, fusiblematerial defining positioning means onsaidsupports, means for spacing said supports apart from each other, and ahelix of grid wire wound about said supports, said grid wire beinginterposed between adjacent turns of said thin fusible material.

8. The method of fabricating a grid assembly for space discharge deviceswhich comprises'the steps of winding a helix of a fusible materialaround each of a pair of support members, securing a plurality of crossstraps to said pair of support members to form a rigid frame assembly,

- winding a helix of grid wire around said frame assembly,

stood by those skilled in the art that various modifications may be madein the materials, shape of grid frame, winding method and processing toachieve the results of the invention.

What is claimed is:

1. The method of fabricating a grid assembly of the said grind wirebeing'positioned by the adjacent turns of a said fusible material, andheating the:frame assembly to fuse said fusible material and secure thegrid wire to the supportmembers inthe desired spaced relation.

9. The method of manufacturing anelectrode structure which comprisesthe. steps of winding a thread of fusible material abouta pairof-support members, the adjacent turns of said thread defining .aplurality of spacestherebetween, connecting a. pair of strap.memberstosaid type including a frame having a pair of side supportmembers which comprises the steps of winding a helix of fusible materialabout each of said support members, said helix defining a plurality ofspaces between adjacent ones of'the turns of said thin fusible material,winding a helix of grid wire upon said support members, said grid wirebeing'positioned in said spaces, and heating the grid assembly to causethe fusible material to fuse and bond the grid wire to said supportmembers.

2. The method of fabricating an electrode assembly for space dischargedevices comprising winding a plusupport members to form an integralframe assembly, winding a plurality of turnsof grid wire around saidframe assembly, said grid wire beingpositioned. in the spaces defined bythe turns of said thread, and heating a the frame assembly to causesaidthread tofuse and bond the grid wire to said support members.

References Cited in the file of this patent UNITED STATES PATENTS

